On Wed, Apr 12, 2023 at 1:02 PM Jason McKesson via Std-Proposals <std-proposals@lists.isocpp.org> wrote:
The other elephant in the room is that SIMD often requires specific
alignment for its objects. And C arrays don't come with that; you'd
have to explicitly align them with `alignas`. Which means you now have
to know what alignment to use for the platform, or to use some type
that provides the alignment (which will often require you to restate
the size of the array).

Whereas with a proper, dedicated type, alignment comes for free.

I think a vectorized CPU would still be able to copy the elements of an unaligned array with the same speed though, right?

If not I guess the requirement would have to be "a list of 2, 4, or 8 floats or ints with no byte padding".